The present disclosure is directed to methods and apparatus for localized heating of glass, such as for deformation of glass sheets during a manufacturing process. For example, the disclosure includes details relating to supporting and accurately positioning a large area glass sheet for high precision bending thereof.
Glass components produced via reforming of initial material parts, such as glass sheets, have many applications, a significant one being glazing for the automotive industry. Reformed glass sheets are also used in display applications, for example in producing liquid crystal displays (LCDs), electrophoretic displays (EPD), organic light emitting diode displays (OLEDs), plasma display panels (PDPs), or the like. For example, electronic devices often include a protective cover glass that provides impact and scratch resistance to the front, display or touch control portion of the device.
Prior to reforming, glass sheets are commonly fabricated by flowing molten glass to a forming body whereby a glass ribbon may be formed by a variety of ribbon forming process techniques, for example, slot draw, float, down-draw, fusion down-draw, or up-draw. The glass ribbon may then be subsequently divided to provide sheet glass suitable for further processing into intermediate shapes for final products. There has been a growing interest in extremely high quality, thin glass sheets that are reformed into more complex three dimensional shapes, such as a combination of flat portions and highly curved edges.
The common processes used to reform glass sheets often involve a heating step at temperatures where deformation occurs under gravity or under mechanical actuation. Heating of a glass sheet using conventional techniques involves application of heat to the entire glass sheet. For example, known means for achieving heating of a glass sheet for reforming include the use of metal-based wires wound around a ceramic support. However, such techniques have not heretofore been satisfactory because heating of the entire glass sheet is not necessarily a desirable result, especially in a reforming operation where only local deformations are needed (e.g., at the edges) and heating of other portions of the glass sheet could result in damage and/or degradation of physical, optical and/or electrical characteristics.
Advancements in reforming processes have been made in order to provide techniques to heat a specific, localized area of a glass sheet in order to achieve formability at the specific location. While such advancements have been substantial, there are still improvements that need to be made. Specifically, very tight tolerances are required in high temperature, glass reforming processes. Even for large consumer electronic devices, such as appliance or LCD devices, there are needs for significantly tight tolerances at 600° to 700° C. local heating temperatures. In many areas of application, tolerances may be on the order of +/−0.2 mm to +/−0.5 mm, depending on the overall dimensions of the glass sheet, which may include a major dimension on the order of about 1.8 meters or more. Such tight tolerances are required for acceptable fit and finish when assembled with other parts of an overall product.
At such high temperatures, however, management of tight tolerances is difficult to achieve, and requires very accurate tuning devices that are capable of operating in a reliable and consistent manner over time. For example, meeting the tolerances requires very precise and repeatable positioning of the local heating elements and/or any bending force elements with respect to the glass sheet. Without such accuracy, it would be very difficult or impossible to achieve repeatable dimensions in the final product, especially in mass production.
Thus, there are needs for methods and apparatus for accurate and precise positioning of any localized heating elements and/or bending force elements in a glass reforming system in order to retain a high level of flatness in desired areas of the glass sheet; retaining pristine aspects of the glass sheet; obtaining a desired amount of deformation in certain areas of interest; and maintaining a high level of dimensional control.